Temperament traits and microhabitat use in bullhead, **Cottus perifretum** : fish associated with complex habitats are less aggressiveTemperament traits and microhabitat use in bullhead, **Cottus perifretum** : fish associated with complex habitats are less aggressive

Temperament traits have been linked to fitness-related functional contexts such as dispersal or mating attractiveness, but few studies have linked inter-individual differences in habitat use to temperament traits. Therefore, we conducted a three-month field study with weekly tracking to define the individual microhabitat use of bullhead (Cottus perifretum). The species is known for its dependence on structured habitats. At the end of the field-survey, bullhead were recaptured and tested in the laboratory for five temperament traits: boldness, interest in novel food, novel environment activity, aggressiveness and activity. Repeated trait tests (activity, r = 0.439; novel environment activity, r = 0.422) and habitat complexity use (r = 0.568) indicated behavioural consistency. Overall, bullhead significantly preferred complex habitats, such as branch jams, while avoiding open water. Individual frequency in the use of complex habitats could not be attributed to size or sex differences, but was significantly negatively correlated to the level of aggressiveness. We hypothesize that this relationship was caused by a higher level of aggressive defence of less structured territories. Other temperament traits were not significantly linked to individual habitat use. To our knowledge, this study is the first to show a relationship between aggressiveness measured under laboratory conditions and the use of complex habitats in situ.